Conjugated heat transfer in a concentric annular pipe

Combined convection and radiation heat transfer for adsorbing-emitting gas in the entrance region of a finite length concentric annular duct is numerically investigated. The thermal boundary conditions imposed on the two duct walls are of a mixed type; a constant heat flux, attributed by both radiation and conduction, is imposed at the inner wall, and a constant temperature is imposed at the outer wall. An approximation model, namely the method of moments, is employed to consider the radiation contribution. The method of lines (MOL) is employed to discretize the nonlinear partial differential energy and radiation transport equations into a set of ordinary differential equations. The fifth-order Runge-Kutta-Verner method is used to solve the ordinary differential equation set. The effects of six major parameters on the conjugate behavior in the entrance region of a concentric annular duct are discussed. Compared to the isothermal boundary condition, the results indicate that the local Nusselt number exhibits many different behaviors for the mixed boundary condition. (orig.)